I currently have a tank with a male Dwarf Gourami, one yellow male guppy, and three Harlequin Rasboras. After doing some research, people have been saying that male bettas can sometimes be put with fish such as guppies or rasporas, but I'm not able to find if the Dwarf Gourami is compatible. I'm considering getting a black or white full-moon tail betta and seeing if it would work out. If anyone has any experience with this or any insight, it would be awesome.

It's a general rule that you should avoid mixing anabantids like gouramis and bettas--dwarf gouramis can be quite aggressive and territorial much in the same way that bettas are. Since both fish have to go to the surface to breathe, they end up in each other's "territory" frequently and squabble--a halfmoon would not be able to escape the gourami because their finnage is so heavy that they are not fast swimmers. It's not a good idea.

In my experience, some of the more peaceful gouramis can co-exist with more intimidating bettas, I have a small group of sparkling gouramis in with a "king" plakat, but the only reason he isn't nipped by them is because he is large and intimidating, and because his smaller fins allow him to swim away more quickly if necessary. A halfmoon or other longfinned type of betta would probably be nipped severely by them.